Fact Witnesses As Experts: Westerhof v Gee Estate, 2015 ONCA 206

In Westerhof v Gee Estate, the Ontario Court of Appeal decided that participant experts and non-party experts may give opinion evidence without complying with Rule 53.03. In other words, a fact witness who is considered an expert may give opinion evidence without filing an expert report or fulfilling any of the other requirements normally applicable to litigation experts. The decision narrows the scope and application of the rules on experts who are engaged by a party to provide evidence including the requirement to file an expert report.

The decision arises from two cases involving motor vehicle accidents. The question on appeal was whether and to what extent medical witnesses could give opinion evidence at trial. In the one case, the trial judge ruled that medical witnesses, who had treated the plaintiff but did not comply with Rule 53.03, could not give opinion evidence concerning diagnosis or prognosis, even if they had not been retained for the purpose of the